This project investigates the potential of a sperm antigen, ph-20, as an immunocontraceptive in male and female macaques. Ph-20 was first isolated from guinea pig sperm by Dr. Paul Primakoff at the University of Connecticut, and he has now isolated cynomolgus ph-20 and produced rabbit antibodies to CPH-20. The first major effort in this project has been ph-20 localization and characterization of ph-20 function in macaque sperm. Fluoresence microscopy and transmission electron microscopy (TEM) were used to determine the location of the membrane ph-20 on macaque sperm. Rabbit antiserum raised to CPH-20 was used as the primary antibody and the second antibody was goat-anti rabbit IGG conjugated with either fitc or gold particles. Sperm were evaluated before and after capacitation and induction of acrosome reactions with calcium ionophore a23187. In sperm suspensions with a high percentage of intact acrosomes, fluorescence labeling of the posterior sperm head was greatly reduced. Tem of acrosome-intact sperm revealed gold particles distributed uniformly on the plasma membrane overlying the acrosome, the equatorial segment, and most of the post-acrosomal region. After the acrosome reaction, gold label was present on the inner acrosomal membrane and on the plasma membrane overlying the equatorial segment. Very little label was present on the plasma membrane in the post-acrosomal region of acrosome-reacted sperm. The location of ph-20 on the surface of macaque sperm suggests a function for this protein in primary and/or secondary binding to the zona. The apparent decrease in amount of ph-20 on the posterior head of macaque sperm following the acrosome reaction is consistent with the migration of this protein to the inner acrosomal membrane, as demonstrated previously for the homologous ph-20 protein of guinea pig sperm.